The present invention relates to sewing machine speed control systems, and in particular to a digital sewing machine speed control system in which machine speed is controlled in response to a digital speed setting signal. This invention is particularly advantageous to microcomputer applications and also to manual selection of a desired operating speed characteristic to meet specific sewing machine operation.
A conventional sewing machine speed control system includes an analog circuit that generates an analog speed setting signal in response to depression of a foot pedal. The analog speed setting signal is typically generated by a magnetic sensor located with respect to a permanent magnet which is mounted for movement with the foot pedal, whereby the depression of the pedal results in variation in the amplitude of the output of the sensor.
It is of particular importance that the sewing machine speed be varied with precision in response to a small change in pedal depression. Further, machine speed is varied according to a predetermined operating characteristics. It is often desired that such operating characteristics be manually selected to meet specific operating needs.
However, it would be almost impossible for conventional analog speed control system to achieve precision speed control as well as manual selection of operating characteristics. Further, the analog system is not adaptable to integrated-circuits and to microcomputer applications.
Sewing machine control circuits usually include varied control functions other than speed control functions. To meet these functions, microcomputers are extensively employed not only because of their multi-function capabilities but because of reduction of component parts with a consequential reduction of cost.